On the fly write head flyheight detector

ABSTRACT

Embodiments of the invention measure a flying height of a recording head. According to one embodiment, in a magnetic circuit comprising a recording head and a magnetic disk, a magnetic resistance changes when a flying height of a recording head fluctuates. A change in an impedance of a recording circuit is measured by making use of a recording current flown in a recording head when recording data indicates a change of a flying height of the recording head during data recording. The measured flying height can be used for stabilizing a recording operation in the magnetic disk device. This method is especially effective in a magnetic disk device based on the perpendicular magnetic recording system because an impedance largely changes in this type of magnetic disk device.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.JP2005-012275, filed Jan. 20, 2005, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a technique for measuring a flyingheight of a recording head in a magnetic disk device, and moreparticularly to a technique for measuring a flying height of a recordinghead to execute recording operations in the stable state.

In a magnetic disk device, a magnetic head floats over a magnetic diskas a recording medium to record data at or reproduce data stored at aspecified position of the magnetic disk. The magnetic head is embeddedin a slider, and the magnetic head and the slider form a head/slider.The head/slider is attached to a suspension assembly and is positionedby an actuator on a specified position in the radial direction of themagnetic disk.

Recent magnetic heads have the structure in which an MR head or a GMRhead constituting a reproduction element and an induction type of headconstituting a recording head are separated from each other and areembedded in the same slider. The head/slider receives a buoyancy by anair flow generated on a surface of the turning magnetic disk with an airbearing surface (described as ABS hereinafter) which is a surface facingagainst the magnetic disk and floats over the magnetic disk. A physicalclearance between the head/slider and a magnetic disk surface or arecording layer surface is generally called flying height.

Recently, in order to improve the recording density in a magnetic disk,attempts have been made to reduce a flight height of a head/slider, andmonitoring and control over a flying height have become more and moreimportant. A flying height depends on a form of an ABS of a head/slider,a mechanical structure of a suspension assembly supporting thehead/slider, flatness of a surface of a turning magnetic disk and otherfactors, so that the flying height cannot be constant. When the flyingheight is too low, however, the ABS may collide with dust and the likeon the magnetic disk, and a floating posture of the head/slider losesthe stability, or collision between the magnetic disk and magnetic headmay occur. When the flying height is too high, a magnetic coupling forcebetween the magnetic head and the recording layer becomes weaker, andthe recording or reproduction capability is degraded.

A flying height fluctuates even after shipment of a magnetic disk devicedue to such factors as distortion of the suspension mechanism acrossages and also to environmental conditions for use thereof such as atemperature or an atmospheric pressure. It is difficult to measure aflying height in a shipped magnetic disk device with a specific device,but the technique for measuring fluctuations of a flying height byprocessing a signal reproduced from a magnetic disk with a reproductionhead is described in patent document 1 (Japanese Patent Laid-Open No.2001-195211). Patent document 2 (Japanese Patent Laid-Open No.2004-281012) discloses a technique for controlling a recording currentto cope with fluctuations of a flying height due to thermal expansiongenerated in a recording head by a recording current. Patent document 3(Japanese Patent Laid-Open No. Hei 5-20635) discloses a technique forcontrolling a projection rate of a tip section of a magnetic polar dueto thermal expansion by energizing a resistance body embedded around athin film magnetic head element for heating it.

BRIEF SUMMARY OF THE INVENTION

Other than the method described in patent document 1, there is also thetechnique for measuring a flying height of a reproduction head by payingattention to change in frequency components of a reproduction signal fordata recorded in a magnetic disk according to a flying height. However,although a recording head and a reproduction head are embedded in thesame slider, there is a prespecified space between the recording headand the reproduction head. Because of this configuration, a spacebetween the recording head and the reproduction head in the radialdirection of the magnetic disk when the reproduction head is positionedat a prespecified position on the magnetic disk may sometimes correspondto several tracks or several tens of tracks apart due to the so-calledyaw angle.

Therefore, a flying height measured by analyzing a reproduction signalis equivalent to a value based on a flying height of a reproductionhead, but it cannot be said that the value is directly related to aflying height of a recording head. Further, even if one tries toestimate a flying height of a recording head when user data is beingrecorded in a magnetic disk from a flying height of a reproduction head,when the recording head is positioned on a recording position on amagnetic disk, the reproduction head is not always positioned at acenter of a servo track or a center of a pattern to be measured, andtherefore even though a reproduction signal is analyzed for the purposeto measure a flying height of the recording head, sometimes a flyingheight of the reproduction head cannot always be measured.

When servo data is utilized for measuring a flying height with areproduction head, as servo data is written in servo tracks discretelyarranged on a magnetic disk in the circumferential direction, so that,when the reproduction head floats between servo tracks, the flyingheight cannot be measured. Further sometimes the thermal protrusion orthermal expansion of a recording head which are factors completelyindependent from a floating rate of a head/slider may have someconnections with a flying height of the recording head, and thereforeaccurate measurement of a flying height of a recording head has beendesired. If a flying height of a recording head can accurately bemeasured, it becomes possible to improve reliability in data recording,for instance, by stopping a recording operation or controlling a flyingheight when the flying height is in the unstable condition.

To solve the problems as described above, it is a feature of the presentinvention to measure a flying height of a recording head. It is anotherfeature of the present invention to provide a method of measuring aflying height of a recording head by making use of an impedance of arecording circuit comprising a recording head and wiring. It is stillanother feature of the present invention to provide a recording methodwith high reliability by measuring a flying height of a recording head.Further it is another feature of the present invention to provide amagnetic disk device capable of executing the method.

A principle of the present invention resides in that, for the purpose tomeasure a flying height of a recording head, a current is flown througha recording circuit consisting of a recording head and wiring to measurean impedance thereof. As an impedance of a recording circuit changes dueto fluctuations of a flying height, also the current flowing through therecording circuit changes according to fluctuations of a flying height.By making use of this characteristic, it is possible to measure a flyingheight of a recording head from an impedance of the recording circuitmeasured based on a value of a current flowing through the recordingcircuit.

In this specification, a flying height is defined as a physical distancebetween a prespecified place on an ABS of a head/slider of a recordinghead or a reproduction head and a prespecified place on a protectionfilm surface or a magnetic layer surface of a magnetic disk. The flyingheight means not only a physical distance but also means arepresentative value representing a flying height in some meaning orother, for instance, in a case where a flying height is expressed as apercentage against a reference value, or in a case where the term isused to represent some other performance relating to a flying heightsuch as an impedance.

A first aspect of the present invention is a method of measuring aflying height of a recording head in a magnetic disk device, and thismethod comprises the steps of flowing a recording current in a recordingcircuit comprising said recording head and wiring connected to therecording head to record data in said magnetic disk, and measuring aflying height of the recording head from an impedance of the recordingcircuit obtained based on a value of the recording current.

In this first aspect, as a value of an impedance of a recording circuitobtained from a current flowing through the recording circuit is used,the measured flying height indicates that of the recording head or thatdirectly connected to the recording head. Further when not a testcurrent for measurement but a recording current for recording user datais flown through the recording circuit, a flying height of the recordinghead can be measured while recording the user data. When the magneticdisk device employs the perpendicular magnetic recording system, as achange rate of an impedance of a recording circuit against fluctuationof a flying height is larger as compared to that in a magnetic diskdevice based on the intra-surface magnetic recording system, andtherefore the measurement precision can be improved.

A second aspect of the present invention is a method of recording userdata with a magnetic disk device having a head/slider with a recordinghead formed thereon and a magnetic disk including a vertical recordinglayer, and this method comprises the steps of supplying a recordingcurrent to a recording circuit comprising the recording head and wiringconnected to the recording head to start an operation for recording userdata in the magnetic disk, measuring a flying height of the recordinghead from an impedance of the recording circuit obtained based on avalue of the recording current, and stopping the recording operationbased on the flying height.

When the measured flying height indicates any abnormality, it ispossible to prevent from recording data at an erroneous position orperforming an incomplete recording operation by stopping the recordingoperation. Further by restarting the recording operation when the flyingheight returns to the normal state, it is possible to maintaincontinuity of data recording when the head/slider collide with dust orany other foreign material on the magnetic disk and the flying heightbecome transitionally abnormal.

A third aspect of the present invention is a method of recording userdata with a magnetic disk device having a head/slider with a recordinghead formed thereon and a magnetic disk including a vertical recordinglayer, and this method comprises the steps of supplying a recordingcurrent to a recording circuit comprising the recording head and wiringconnected to the recording head to start an operation for recording userdata in the magnetic disk, measuring a flying height of the recordinghead from an impedance of the recording circuit obtained based on avalue of the recording circuit, and adjusting a flying height of therecording head based on the flying height obtained as described above.

A fourth aspect of the present invention provides a magnetic disk devicecomprising a magnetic disk, a head/slider having a recording head forrecording data in the magnetic disk formed thereon, wiring connected tothe recording head, a head driver for generating a recording current tobe supplied to the recording head, and a flying height measuring circuitconnected to the head driver as well as to the wiring for measuring animpedance of a recording circuit comprising the wiring and recordinghead from a recording current flowing through the wiring and outputtinga flying height of the recording head.

With the present invention, it is possible to provide a method ofmeasuring a flying height of according to a recording head. With thepresent invention, it is possible to provide a method of measuring aflying height of a recording head by making use of an impedance of arecording circuit comprising a recording head and wiring. With thepresent invention, it is possible to provide a recording method with ahigh reliability by measuring a flying height of a recording head.Further with the present invention, it is possible to provide a magneticdisk device capable of executing the methods described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematically showing a magnetic disk based on theperpendicular magnetic recording system and a magnetic head.

FIG. 2 is a view showing an equivalent circuit of a recording circuit inwhich a recording current flows from an head amplifier to a recordinghead.

FIG. 3 is a view showing a first example of a flying height detectioncircuit.

FIG. 4 is a view showing a frequency spectrum of a voltage generated inthe recording circuit.

FIG. 5 is a view showing a second example of the flying height detectioncircuit.

FIG. 6 is a view for illustrating operations of an integration circuit.

FIG. 7 is a block diagram showing a key section of a magnetic diskdevice.

FIG. 8 is a block diagram showing a head amplifier according to anembodiment of the invention.

FIG. 9 is a flow chart illustrating a method of stabilizing a recordingoperation according to an embodiment of the invention.

FIG. 10 is another block diagram showing the head amplifier according toan embodiment of the invention.

FIG. 11 is a flow chart illustrating a method of controlling a flyingheight according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Principle of Flying Height Measurement

FIG. 1 is a side view schematically showing a magnetic disk based on theperpendicular magnetic recording system and a magnetic head. Themagnetic head is formed in a slider not shown as a hybrid type of headcomprising a recording head 11 and a reproduction head 12 which areseparated from each other. The recording head 11 comprises a mainmagnetic pole 13 comprising a magnetic thin film with high magneticpermeability, an auxiliary pole 15 and a thin film coil 17. Thereproduction head 12 comprises an upper shield also used as an auxiliarymagnetic pole 15, a lower shield 19, and a GMR reproduction element 21provided therebetween. A write gap between the main magnetic pole 13 andthe auxiliary magnetic pole 15 in the recording head 11 is wider ascompared to that in a ring type of recording head for intra-surfacemagnetic recording.

In a case of a magnetic disk 27 for perpendicular magnetic recording, asoft magnetic layer 31 with high magnetic permeability and a verticalrecording layer 29 made of such a material as CoCrPt are laminated on asubstrate (not shown) made of such a material as glass or aluminum, anda protection layer or a lubrication layer (both not shown) is formed onthe vertical recording layer 29. When a recording current is supplied toa coil 17 of the recording head 11 from a head amplifier providedseparately, a synthesized magnetic flux 23 comprising an effectivemagnetic flux 22 and a leak magnetic flux 25 synthesized with each otherflows in the main magnetic pole 13 as well as in the auxiliary magneticpole 15. The effective magnetic flux 22 coming out of an edge of themain pole passes through the gap 26, vertical recording layer 29, softmagnetic layer 31, and a gap 28 and returns to the edge section of theauxiliary pole 15, while the leak magnetic flux 25 flows between an edgeof the main magnetic pole 13 and an edge of the auxiliary magnetic pole15. The effective magnetic flux 22 contributes to magnetic recording inthe vertical recording layer 29, but the leak magnetic flux 25 does notcontribute to magnetic recording.

The gaps 26, 28 correspond to a flying height of the recording head. Thevertical recording layer 29 is a vertically anisotropic magnetic layerwhich is easily magnetized in a direction perpendicular to a surface ofthe magnetic disk. The effective magnetic flux 22 coming out of an edgeof the main magnetic pole 13 to the gap 26 easily passes through thesoft magnetic disk 31, so that the effective magnetic flux 22 passesthrough the vertical recording layer 29 in the vertical direction andmagnetizes the vertical recording layer 29 in the vertical direction.When a flying height of the recording head 11 fluctuates, also a spacebetween the gaps 26, 28 fluctuates. When a space between the gaps 26, 28becomes larger, a magnetic resistance of a magnetic circuit throughwhich the effective flux 22 passes through becomes larger, so that theeffective magnetic flux 22 decreases, whereas, when a space between thegaps 26, 28 becomes smaller, a magnetic resistance of the magneticcircuit becomes smaller, so that the effective magnetic flux 22increases. Even if the gaps 26, 28 fluctuate, the leak magnetic flux 25changes little.

Fluctuations in a flying height of the recording head 11 appear as thoseof a magnetic flux flowing through the magnetic circuit of the recordinghead 11, which can electrically be detected as fluctuations in a selfinductance of the coil 17 or as those in an impedance of the recordingcircuit. In the present invention, it was found as a result ofsimulation that a fluctuation rate of the self inductance is around 10%at the upper limit as well as at the lower limit of a flying height, andtherefore detection of a fluctuation rate in a self inductance canpractically be used for detection of a flying height.

FIG. 2 is an electrically equivalent circuit 40 of the recording circuitfrom the head amplifier via the wiring to the coil 17 of the recordinghead 11. The equivalent circuit 40 comprises a plurality of impedanceelements. The sign s used for designating an impedance element indicatesa Laplace operator, and s is equal to jω and therefore to 2πf (j is animaginary unit, and f indicates a frequency of a current) (s=jω=j2πf).L₁ and R₁ indicate an inductance of a wiring path from a head amplifierto a coil in a recording head and a resistance respectively. C indicatesa capacitance including those of the recoding head and the wiring path.L and R₂ indicate a self inductance and a resistance of the recordinghead 11. For the equivalent circuit shown in FIG. 2, an impedance Z inthe recording head 11 when viewed from the head amplifier is asexpressed by Equation 1 shown below because of the relation of V=ZI;$\begin{matrix}{Z = \frac{\begin{matrix}{R_{1} + R_{2} + {\left( {L + L_{1} + {{CR}_{1}R_{2}}} \right)s} +} \\{{\left( {{CLR}_{1} + {{CL}_{1}R_{2}}} \right)s^{2}} + {{CLL}_{1}s^{3}}}\end{matrix}}{1 + {{CR}_{2}s} + {CLs}^{2}}} & \left( {{Equation}\quad 1} \right)\end{matrix}$wherein V indicates a voltage loaded to the recording head 11 measuredat an output terminal of the head amplifier, and I indicates a recordingcurrent.

Of the components of the impedance Z of the equivalent circuit 40, L₁,R₁, and C change little after production. A value of a coil resistance Rin the recording head 11 fluctuates under the influence of a recordingcurrent or a temperature in the environment for use of the magnetic diskdevice because the value changes according to a temperature of the coil,while the self inductance L fluctuates under the influence of a flyingheight of the recording head 11. Therefore, by preparing a parametertable in which mutual relations between a flying height of the recordinghead 11 measured by the known method such as by using a laser beam orthe like and the recording current I, a temperature of the environmentfor use thereof, and the impedance Z of the equivalent circuit isrecorded, and also by dynamically measuring the impedance Z while datais written with the recording head and referring to the parameter table,a flying height of the recording head during the operation for recordinguser data or test data can be obtained.

A method of measuring a flying height by measuring an impedance of arecording circuit 41 based on a recording current applying the spectrummethod is described below with reference to FIG. 3. A head amplifier 50is a component of a magnetic disk device, and comprises a head driver51, a spectrum voltage generating section 53, a computing section 55,and a parameter table 57. The recording circuit 41 comprises a wiringpath from the head amplifier 50 to the recording head 11 and animpedance of the recording head 11, and can be expressed with theequivalent circuit 40 shown in FIG. 2. The spectrum voltage generatingsection 53, computing section 55, and parameter table 57 form a flyingheight measuring circuit.

The head driver 51 receives a data signal modulated by a read/writechannel (described as R/W channel hereinafter) of a magnetic disk devicevia a terminal 52, and generates a recording current to be supplied tothe recording head 11 of the recording circuit 41. The recording currentis expressed mainly with a rectangular waveform, and includes harmoniccomponents of up to around 1 GHz against the basic frequency of around100 MHz. The spectrum voltage generating section 53 generates afrequency spectrum of a voltage at an input terminal 56 of the recordingcircuit 41 when a recording current is supplied to the recording head11. A recording current includes current components having variousfrequencies respectively, and a voltage at the input terminal 56 of therecording circuit 41 when the recording current is supplied to therecording circuit 41 includes various voltage components having variousfrequencies respectively. FIG. 4 is a view showing a frequency spectrumof a voltage at the input terminal 56 of the recording circuit 41. FIG.4 shows a spectrum voltage according to a line 61 as a voltage V1 forthe basic frequency f1 and spectrum voltages V2 to V6 for frequencies f2to f1 each by an integral number larger as compared to f1 respectively.

An amplitude of a harmonic component included in a recording currentbecomes smaller as the frequency is higher, so that there is thetendency that the spectrum voltage becomes smaller as the frequency ishigher. Further, because of the relations expressed by Equation 1 andV=ZI, when a flying height of the recording head 11 shown in FIG. 1 ishigher, the self inductance L of the recording head 11 is smaller, sothat an amplitude of the harmonic component in the spectrum voltagebecomes smaller as shown by the line 65, and when the flying heightbecomes lower, the self inductance L will become larger with theamplitude of the harmonic wave portion in the spectrum voltage becominglarger. An amplitude of the basic frequency or of a relatively lowfrequency close to the basic frequency changes little even when theflying height fluctuates, so that the sensitivity to the flying heightis rather low. A magnitude of a change in a spectrum voltage caused byfluctuation of a flying height is described herein as FH sensitivity.

A percentage of a change in an amplitude of a spectrum voltagecorresponding to the harmonic component under the influence by a changein the self inductance L of a recording head is not always constant forall of the spectrum voltages V2 to V6, and a spectrum voltage having aspecific frequency showing the high FH sensitivity. The FH sensitivityof each spectrum voltage changes according to the impedanceconfiguration of the recording circuit 41, so that the change ratesshould be examined previously in a test process. In the followingdescription, a spectrum voltage having a specific frequency componentselected from the spectrum voltages having high FH sensitivitiesrespectively is described as a detected spectrum voltage Vx, and aspectrum voltage with low FH sensitivity is described as a referencespectrum voltage Vb.

The spectrum voltage generating section 53 can be formed with a combfilter or a band pass filter with a narrow band width. The spectrumvoltage generating section 53 generates a reference spectrum voltage Vband at least one detected spectrum voltage Vx. When a comb filter isused, the reference spectrum voltage Vb and detected spectrum voltage Vxcan easily be generated by setting a delay time. The spectrum voltagegenerating section 53 may be either an analog circuit or a digitalcircuit, but an analog circuit is preferable because the operating speedis higher.

The computing section 55 computes a Vx/Vb based on the referencespectrum voltage Vb and detected spectrum voltage Vx received from thespectrum voltage generating section 53 and refers to the parameter table57. The parameter table 57 stores therein data for flying heightsindicating a relation between the Vx/Vb and a flying height of therecording head 11 tested and confirmed in a test process beforeshipment. When a magnetic disk device comprises a plurality of recordingheads, the parameter table 57 stores therein flying height data for eachrecording data.

The computing section 55 refers to and fetches a flying height from theparameter table 57 based on the computed Vx/Vb value, and sends a flyingheight signal from an output terminal 54 to an MPU unit in the magneticdisk device. The computing section 55 and parameter table 57 may beprovided not only in the head amplifier 50 but in the MPU unit.

A method of measuring a flying height by detecting an impedance of therecording circuit 41 by means of the model matching method is describedwith reference to FIG. 5. A head amplifier 70 is a component of amagnetic disk device, and comprises a head driver 71, a differentialcurrent integration circuit 73, simulation circuit 77, animpedance-matching section 75, and a parameter table 79. Thedifferential current integration circuit 73, impedance-matching section75, and simulation circuit 77 form a flying height measuring circuit.

A head driver 71 receives recorded data modulated by the R/W channel viaa terminal 72, and loads the same voltage to the recording circuit 41and to the simulation circuit 77. The recording circuit 41 can beexpressed by the equivalent circuit 40 shown in FIG. 2, and when avoltage is loaded thereto from the head driver 71, the recording currentI1 flows through the recording circuit 41. The simulation circuit 77includes a component for an impedance or a transfer function Zmsatisfying Equation 2 in correspondence to the equivalent circuit 40expressed by Equation 1. $\begin{matrix}{{Zm} = \frac{q_{0} + {q_{1}s} + {q_{2}s^{2}} + {q_{3}s^{3}}}{1 + {p_{1}s} + {p_{2}s^{2}}}} & \left( {{Equation}\quad 2} \right)\end{matrix}$

Equation 1 and Equation 2 have the relationships as indicated byEquations 3 through 6:q0=R ₁ +R ₂  Equation 3q1=L+L ₁ +CR ₁ R ₂  Equation 4q2=CLR ₁ +CL ₁ R ₂  Equation 5q3=CLL ₁  Equation 6

Therefore, by appropriately selecting a component for an impedance ofthe simulation circuit 77, it is possible to match the recording currentI1 flowing through the recording circuit 41 to a simulation current 12flowing through the simulation circuit 77. Values of the impedanceelements q0 to q3 of the simulation circuit 77 can be changed accordingto a signal from the impedance-matching section 75. The differentialcurrent integration circuit 73 comprises an analog circuit or a digitalcircuit, detects the current I1 flowing through the recording circuit 41and the simulation current I2 flowing through the simulation circuit 77,and integrates the difference once for a prespecified period of time.

FIG. 6 is a view illustrating operations of the differential currentintegration circuit 73. As shown in the initial state of the elapsedtime in FIG. 6(A), the recording current I1 and simulation current I2generally take different values respectively unless the impedanceelements q0 to q3 are adjusted. FIG. 6(A) shows a case where a value ofthe simulation current I2 is larger than a value of the recordingcurrent I1, but a value of the simulation current I2 may be smaller thanthat of the recording current I1. FIG. 6(B) shows the state where thedifferential current integration circuit 73 computes an integrated valueof a value indicating a difference between the recording current I1 andthe simulation current I2 once for every prespecified period of time Δtand accumulates the values. The differential current integration circuit73 further computes change rates ΔI1 to ΔI4 of the integrated values andsuccessively sends the computed change rates to the impedance-matchingsection 75.

When the change rate ΔI is larger than a prespecified threshold value,the impedance-matching section 75 generates an operation signal forchanging each of the impedance elements q0 to q3 and sends the signal tothe simulation circuit 77. The algorithm for changing the impedanceelements q0 to q3 for converging the simulation current I2 to therecording current I1 is decided by making use of any known method suchas the experiment planning method. When the impedance elements q0 to q3are approximated to the corresponding values for the recording circuit41 by operation signals from the impedance-matching section 75, thesimulation current 12 converges to the recording current I1 with thedifference ΔI of the integrated value gradually reduced even below thethreshold value.

At this point of time, assuming that the recording current I1 is equalto the simulation current I2, it can be considered that the impedance Zof the recording circuit 41 has matched the impedance Zm of thesimulation circuit 77. The parameter table 79 stores therein dataindicating relations between the impedance elements q0 to q3 of thesimulation circuit 77 previously measured in the test process andrepresentative values of flying heights. When the magnetic disk devicehas a plurality of recording heads, the parameter table 79 stores theflying height data for each of the recording heads. Theimpedance-matching section 75 computes values of the impedance elementsq0 to q3 from values of operation signals to the simulation circuit 77when the difference ΔI of the integrated value is below the thresholdvalue, obtains values of the flying heights by referring to theparameter table 79, and sends flying height signals from an outputterminal 74 to the MPU. The impedance-matching section 75 and parametertable 79 may be realized with an MPU unit in the magnetic disk device.

General Configuration of a Magnetic Disk Device

FIG. 7 is a general block diagram showing a magnetic disk device 100comprising the circuit for measuring a flying height of a recording headas described above. The magnetic disk device 100 comprises two sheets ofmagnetic disks 111, 112 for perpendicular magnetic recording. Themagnetic disk 111 comprises recording surfaces 111 a, 111 b, and themagnetic disk 112 comprises recording surfaces 112 a, 112 b. Maincomponents of each recording surface include a protection layer, avertical recording layer, and a soft magnetic layer each formed on asubstrate. The magnetic disks 111, 112 are fixed to a spindle shaft 115with a prespecified space therebetween, and are simultaneously rotatedby a spindle motor (described as SPM hereinafter) 113.

Provided in the magnetic disk device 100 are four head/sliders 117 a,117 b, 117 c, 117 d corresponding to the recording surfaces 111 a, 111b, 112 a, 112 b respectively. Formed in each head/slider is a magnetichead comprising an induction type of head for recording and a GMR headfor reproduction which are integrated into a hybrid type of head. Thehead/sliders 117 a, 117 b, 117 c, 117 d are attached to head supportmechanisms 125 a, 125 b, 125 c, and 125 d respectively. The head supportmechanism comprises a flexure, suspension assembly, a carriage, and avoice coil motor (described as VCM hereinafter) 119, and positions eachmagnetic head at a prespecified position on a corresponding magneticdisk.

A head amplifier 121 is attached to the head support mechanism. Thetechnique for attaching a head amplifier to the head support mechanismis generally known as chip on suspension (COS) or arm electronics (AE).The head amplifier 121 comprises a read/write driver (described as R/Wdriver hereinafter), a driver register, a read/write switching circuit(described as R/W switching circuit), and a flying height measuringcircuit which is a main component for realizing the present invention,and the components are described in detail hereinafter.

Further the magnetic disk device 100 comprises a circuit board 127 witha R/W channel 129, an MPU unit 131, a power/driver 135, a hard diskcontroller (HDC) 137, and a buffer memory 141 packaged thereon. The R/Wchannel 129 comprises a modulation circuit for converting a data bitarray to a bit array to be recorded on a magnetic disk and ademodulation circuit for executing conversion in the reverse direction,a parallel/serial converter for converting parallel data to and fromserial data, and a variable gain amplifier (VGA) for adjusting areproduced signal to a constant voltage level.

The MPU unit 131 comprises an MPU for controlling operations of themagnetic disk device 100 as a whole, a ROM for storing therein varioustypes of programs, and a RAM used for execution of the programs or as awork area. The programs include those for measuring a flying height orfor executing a data recording method. The hard disk controller 137comprises a servo controller for controlling a seek operation, a trackfollowing operation and the like based on servo data, a buffercontroller for controlling the buffer memory 141, and an ECC circuit forgenerating corrected bits for data bits sent from a host computer orcorrecting user data reproduced from the magnetic disk. The buffermemory 141 is used for realizing high speed data transfer between thehost computer and the magnetic disk device.

The power/driver 135 comprises an SPM driver for supplying an operatingcurrent to the SPM 113, a VCM driver for supplying an operating currentto the VCM 119, a DA converter, and a power circuit. Further thepower/driver 135 comprises a circuit for supplying a current to a heatercontrol circuit for the heat amplifier described hereinafter. Attachedto the circuit board 127 is an interface connector 139 for datacommunications with the host computer.

Configuration of the Head Amplifier

FIG. 8 is a general block diagram for the head amplifier 121 having aflying height measuring circuit provided therein. An R/W driver 201receives a driver drive current from the power/driver 135 through a line239. The R/W driver 201 comprises write drivers 203, 207, 211, 215, andsupplies a recording current to recording heads of the head/sliders 117a, 117 b, 117 c, and 117 d. The R/W driver 201 further comprises readamplifiers 205, 209, 213, 217, supplies a bias current to reproductionheads of the head/sliders 117 a, 117 b, 117 c, 117 d, and detects achange of an electric resistance by a magnetic field recorded in themagnetic disk to reproduce the recorded data.

The R/W driver 201 has a circuit for generating a rectangular waveformcurrent, a circuit for generating an overshoot current, and a circuitfor synthesizing the currents. The R/W driver 201 can receive a digitalsignal from a driver register 219 and change magnitudes of a componentof the rectangular waveform current and that of the overshoot current inthe recording current discretely. The driver register 219 comprises aregister for storing therein a digital set value concerning arectangular waveform current in a recording current and a register forstoring therein a digital set value concerning an overshoot current.Setting of the driver register 219 is performed by the MPU unit 131 viaa line 241. The R/W switching circuit 235 receives an R/W gate signalconcerning one operation mode of either a recording operation or areproduction operation generated by the HDC 137 via a line 245, andswitches an operation mode of the R/W driver 201 and the R/W buffer 237.

The R/W buffer 237 temporally stores user data therein when transferringthe user data to be recorded or reproduced to and from the R/W channel129 through a line 247. A head select circuit 233 receives a head selectsignal generated by the HDC 137 through a line 243 to activate amagnetic head in any one of the four head/sliders 117 a, 117 b, 117 c,and 117 d.

A flying height measuring circuit 250 is connected to a section betweenthe R/W driver 201 and each of the head/sliders 117 a, 117 b, 117 c, and117 d. The circuit described with reference to FIG. 3 or FIG. 5 may beemployed as the flying height measuring circuit 250, or other knownimpedance measuring circuit may be employed for the same purpose. Theflying height measuring circuit 250 may be provided not in the headamplifier 121, but, for instance, in the MPU unit 131. The flying heightmeasuring circuit 250 measures a self inductance or impedance associatedwith a flying height of a recording head by making use of a recordingcurrent flowing through a recording head of the head/slider selected bythe head select circuit 233 to measure a flying height of the recordinghead.

The recording current for measuring a flying height may be a current forrecording test data or for recording user data. An operation of the R/Wdriver 201 for writing user data or test data in a magnetic disk bysupplying a recording current to a recording head and an operation ofthe flying height measuring circuit 250 for measuring a flying heightare carried out concurrently. Therefore, a value of a flying heightmeasured by the flying height measuring circuit 250 corresponds to aflying height of the recording head when recording data.

The flying height measuring circuit 250 generates a recording headflying height signal (FH signal) and sends the signal through a line 251to the MPU unit 131. Also the configuration is allowable in which theflying height measuring circuit 250 stores a threshold value therein,compares a measured flying height to the threshold value, and sends anFH signal to the MPU unit 131 only when the measured flying height isrecognized as abnormal.

An FH signal concerning a flying height of a recording head may be usedfor various purposes in a magnetic disk device. As one of the causes forabnormality of a flying height of a recording head, collision betweendust deposited on a magnetic disk and a recording head can beconsidered. When data recording is continued in the state where a flyingheight is unstable, the magnetic layer may not sufficiently bemagnetized, or data may be written in an adjoining track, which degradesreliability of the recording operation. In this case, if influence bydust is transitional, it is effective to once stop the recordingoperation and resume the recording operation after the flying height isstabilized.

A method of stabilizing a recording operation by measuring a flyingheight of a recording head in a magnetic disk device 100 connected to ahost computer with an interface connector 139 is described withreference to the related flow chart shown in FIG. 9. In block 301, whenthe magnetic disk device 100 receives a write command and user data froma host computer, the MPU unit 131 sends the user data to the R/W channel129 and controls the R/W channel or the head amplifier 121 for startingthe recording operation. In block 303, the magnetic disk device startswriting the user data in a magnetic disk to which the selected recordinghead corresponds.

In block 305, the flying height measuring circuit 250 starts measurementof a flying height of a recording circuit in which a recording currentflows. The flying height measuring circuit 250 outputs an FH signal whena flying height is off from a prespecified value and abnormal. In block307, when it is detected that a flying height is abnormal, the flyingheight measuring circuit 250 sends an FH signal to the MPU unit 131 inblock 309.

In block 311, the MPU unit 131 having received the FH signal providescontrols over the magnetic disk device for terminating the recordingoperation, and accumulates user data sent from the host computer in thebuffer memory 141 during this period of time. The flying heightmeasuring circuit 250 continues measurement of a flying height evenafter transmission of the FH signal, and when it is determined in block313 that the flying height of a recording head has returned to thenormal state, transmission of the FH signal is stopped in block 315.When the MPU unit 131 recognizes that the FH signal has disappeared, theMPU unit 131 controls the magnetic disk device 100 to resume therecording operation in block 317. Abnormality of a flying height may bedetermined by the MPU unit 131. In this case, the flying heightmeasuring circuit 250 sends a value of a flying height to the MPU unit131.

Next a magnetic disk device capable of controlling a flying height of arecording head by measuring a flying height is described with referenceto FIG. 10. FIG. 10 is a general block diagram showing a head amplifier252 which can be applied to the magnetic disk device 100 in place of thehead amplifier 121 described with reference to FIG. 8. A head amplifier252 has a flying height measuring circuit 260 and is connected tohead/sliders 261 a, 261 b, 261 c, and 261d. Each of the head/sliders 261a, 261 b, 261 c, and 261 d has a heater embedded near a recording headthereof, and by flowing a current through the heater to generate heattherein and control a thermal expansion rate of a magnetic pole of therecording head, a flying height of the recording head can be adjusted.

A heater current is supplied from a heater control circuit 253 to aheater in each head/slider. A heater current is supplied from thepower/driver 135 through a line 257 to the heater control circuit 253.The heater control circuit 253 receives a control signal from the MPUunit 131 through a line 255, and controls a heater current suppliedthrough a line 259 to the head/slider. The flying height measuringcircuit 260 computes a flying height from an impedance of the recordingcircuit obtained based on a value of a recording current when themagnetic disk device starts a recording operation, and sends thecomputed value as an FH signal through a line 263 to the MPU unit 131.Other portions of the head amplifier 252 are the same as those of thehead amplifier 121 shown in FIG. 8.

A method of controlling a flying height of a recording head when themagnetic disk device comprising the head amplifier 252 having theconfiguration as described above is connected to a host computer andcarries out an operation for recording user data is described below withreference to the flow chart shown in FIG. 11. When the magnetic diskdevice 100 receives a write command and user data from the host computerin block 321, the MPU unit 131 sends the user data to the R/W channel129 and provides controls over the R/W channel or the head amplifier 252to start a recording operation, and the magnetic disk device startswriting the user data in a magnetic disk corresponding to the recordinghead selected in block 323.

In block 325, the flying height measuring circuit 260 starts measurementof a flying height based on an impedance of a recording circuit throughwhich a recording current is flowing. The flying height measuringcircuit 260 successively outputs flying height signals to the MPU unit131 through the line 263. In block 327, the MPU unit 131 having receivedflying height signals successively compares each of the received flyingheight signals through the line 261 to a reference value of a flyingheight, and sends a control signal for controlling a heater currentthrough a line 255 to the heater control circuit 253 to adjust theflying height to a value close to the reference value.

More specifically, when a flying height signal received through the line263 is larger than the reference value, the heater current is increasedso that a flying height of a recording head is made smaller, while inturn, when a flying signal is smaller than the reference value, theheater current is reduced so that a flying height of a recording head ismade larger. In this case, not a flying height of the entirehead/slider, but a flying height of only the recording head iscontrolled. The control as described above is possible by measuring aflying height based on an impedance of a recording circuit.

As described above, by dynamically measuring a flying height of arecording head during an operation of recording data and utilizing theresult for controlling a thermal expansion rate of the recording head,it is possible to provide controls with higher precision as compared toa case where indirect parameters for a flying height such as atemperature in an environment for use of a magnetic disk device or atiming for an recording operation are employed for flying heightcontrol. The descriptions for measurement of a flying height aboveassume use of a magnetic disk device based on the perpendicular magneticrecording system and a recording head used in the magnetic disk device,but the principles of the present invention are not limited to theperpendicular magnetic recording system, and are also applicable to theintra-surface magnetic recording system. However, an impedance of arecording circuit including a magnetic disk based on the intra-surfacemagnetic recording system changes only a little according tofluctuations of a flying height, so that a technique for measuring animpedance with high precision is required.

To control a flying height of a recording head, also a method ofcontrolling an ampere of a recording current may be employed. As anampere of a recording current relates to a thermal expansion rate of arecording head, the configuration is allowable in which the MPU unit 131having received a flying height signal changes setting of the driverregister 219 shown in FIG. 10 to control an ampere of the recordingcurrent. More specifically, when a flying height signal having beenreceived through the line 263 is larger than a reference value for aflying height, the MPU unit 131 increases the recording current toreduce a flying height of the recording head, and when the receivedsignal is smaller than the reference value, the MPU unit 131 reduces therecording current to make larger a flying height of the recording head.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reviewing the above description. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

1. A method of measuring a flying height of a recording head in a magnetic disk device, said method comprising: supplying a recording current to a recording circuit including said recording head and wiring connected to said recording head to record data in the magnetic disk; and computing a flying height of said recording head from an impedance of said recording circuit obtained based on a value of said recording current.
 2. The measuring method according to claim 1, wherein said data is user data sent from a host computer.
 3. The measuring method according to claim 1, wherein said magnetic disk has a vertical recording layer.
 4. The measuring method according to claim 1, wherein computing said flying height includes computing a ratio of a voltage component that is fluctuated slightly by a change in an impedance of said recording circuit versus another voltage component that is fluctuated substantially by a change in an impedance of said recording circuit, in a frequency spectrum of a voltage appearing on said recording circuit.
 5. The measuring method according to claim 1, wherein computing said flying height includes changing a value of said variable impedance based on a difference between a value of a current flown in a simulation circuit including a variable impedance and a current value flowing in said recording circuit.
 6. The measuring method according to claim 1, wherein computing said flying height includes referring to a parameter table with flying height corresponding to values of impedances of said recording circuit stored therein.
 7. A method of recording user data in a magnetic disk device including a head/slider with a recording head formed thereon and a magnetic disk including a vertical recording layer, said method comprising: supplying a recording current to a recording circuit including said recording head and wiring connected to said recording head; computing a flying height of said recording head from an impedance of said recording circuit obtained based on a value of said recording current; and stopping said recording operation based on a value of said flying height.
 8. The recording method of claim 7 further including: starting said recording operation based on said flying height in succession to stopping said recording operation.
 9. A method of recording user data in a magnetic disk device including a head/slider with a recording head formed thereon and a magnetic disk including a vertical recording layer, said method comprising: supplying a recording current to a recording circuit including said recording head and wiring connected to said recording head to start an operation for recording user data in said magnetic disk; computing a flying height of said recording head from an impedance of said recording circuit obtained based on a value of said recording current; and adjusting a flying height of said recording head based on said flying height.
 10. The recording method according to claim 9, wherein adjusting a flying height includes controlling a current for a heater provided in said head/slider.
 11. The recording method according to claim 9, wherein adjusting a flying height includes controlling an ampere of said recording current.
 12. A magnetic disk device including: a magnetic disk; a head/slider with a recording head for recording data in said magnetic disk formed therein; wiring connected to said recording head; a head driver configured to generate a recording current to be supplied to said recording head; and a flying height measuring circuit connected to said driver as well as to said wiring for measuring an impedance of a recording circuit including said wiring and said recording head from a recording current flowing through said wiring, and outputting a flying height signal for said recording head.
 13. The magnetic disk according to claim 12, wherein said recording current is a recording current for recording user data in said magnetic disk.
 14. The magnetic disk device according to claim 12, wherein said magnetic disk includes a vertical recording layer.
 15. The magnetic disk device according to claim 12, wherein said flying height measuring circuit includes a spectrum voltage generating section configured to generate a frequency spectrum of a voltage generated in said recording circuit.
 16. The magnetic disk circuit according to claim 12, wherein said flying height measuring circuit has a simulation circuit including a variable impedance corresponding to said recording circuit.
 17. The magnetic disk device according to claim 12, wherein said flying height measuring circuit includes a parameter table with flying heights corresponding to values of impedances of said recording circuit stored therein.
 18. The magnetic disk device according to claim 12, wherein said flying height measuring circuit is formed in a head amplifier mounted in a head support mechanism for said magnetic disk device.
 19. The magnetic disk device according to claim 12 further including a heater for changing a thermal expansion rate of a recording head formed in said head/slider; and a heater control circuit which is controlled according to a control signal generated based on said flying height signal to adjust the heater.
 20. The magnetic disk device according to claim 12 further including: an MPU unit configured to stop a recording operation in response to a flying height signal outputted from said flying height measuring circuit. 